Retractable steps are used in boarding systems for passenger transport vehicles, to make it easier for persons to board and exit. Such retractable steps are also identified as extensions or kick plates. Boarding systems have an extendable retractable step comprising a loadable and walkable tread. The retractable step can thereby be arranged in a frame as accommodating device for the step, which is fixedly connected to the vehicle. For example, the retractable step can thereby be inserted into the frame and can be fastened to the frame for extending the retractable step.
On principle, there are many approaches for designing such boarding systems comprising retractable steps for boarding passenger transport vehicles. It is problematic, however, that tolerances with regard to a distance to the vehicle are at hand due to different boarding platforms, such as, for example train or bus platforms. Known boarding systems can ensure a barrier-free boarding of a vehicle, when a retractable step compensates a distance between the vehicle and a boarding platform, in that the retractable step is extended so that persons can board. However, it is problematic that boarding platforms are designed differently with regard to the distance to the vehicle entrance as well as with regard to the height to the vehicle entrance. This is also why it is necessary for the height of the boarding platform to be compensated with regard to the entrance to the vehicle by means of a boarding aid. This need exists in particular for barrier-free passenger transport entrances.